Mommies out there, what's the best baby formula for the best price?

Alright, I'm pregnant and my sister is living with me with her 2 month old baby girl. Unfortunately I am over qualified for WIC with my husband's income and we have to pay out of pocket for formula. This is no problem but we are both inexperienced since these are our first children. I was wondering if you had any advice on what the best deal on formula is. Any advice is welcomed. Thanks bunches!